You used 'END' where you should have used "END".

print <<END, <<'END', <<"END";
abc\tdef
END
abc\tdef
END
abc\tdef
END
[download]

outputs

abc     def
abc\tdef
abc     def
[download]

<<END is equivalent to <<"END" and not equivalent to <<'END', so the OP needs <<"        END" rather than <<'        END'.